An in-cylinder pressure sensor for the purpose of measurement of in-cylinder pressure of an internal combustion engine is known as disclosed, for instance, in JP-A-2005-291091. There are several types of in-cylinder pressure sensors such as a piezo-electric type in-cylinder pressure sensor in which a piezo-electric element is used as a pressure sensing element or a strain gage type in-cylinder pressure sensor in which a strain gage is used as a pressure sensing element. Generally, these types of in-cylinder pressure sensors are designed, manufactured or installed so that preload is provided to its pressure sensing element for the purpose of high accuracy measurement of in-cylinder pressure when the in-cylinder pressure sensor is attached to an internal combustion engine. A piezo-electric element in the following patent document 1 is attached to a cylinder head of an internal combustion engine so that preload is provided as described above.
Patent Document 1: JP-A-2005-291091
Patent Document 2: JP-A-7-301145
Patent Document 3: JP-A-2007-327502
Patent Document 4: JP-A-2005-330904
Patent Document 5: JP-A-7-29436
Patent Document 6: JP-A-2006-64675